The present invention relates to a refractory gas-permeable structural unit for blowing a gas into a metal treatment vessel and through its casing.
The oxygen top-blowing methods used in pig iron refining, which are known under the names of "LD"-, "LDAC"-, "OLP"-, "BOF"-methods, are recently improved, as far as the metallurgy is concerned, in that secondary gases, such as nitrogen or argon, are blown under controlled conditions through the converter bottom. Also, in other metal treatment vessel like ladles for aftertreatment of steel or electric arc furnaces, the blowing of gas into the metal bath through the bottom of the vessel or the casing of the vessel wall is taken into consideration.
The gas-permeable refractory stones which are inserted into the casing of the bottom or the lateral wall of the vessel to perform the gas supply must satisfy the requirement that their stability must correspond to the stability of the refractory casing, inasmuch as an exchange of the connected gas-permeable stones in hot condition in a vessel bottom is substantially difficult. It is also necessary to provide the gas supply which can be continuous and also discontinuous; in other words, the vessel must be able to operate without gas supply, and after the repeated switching of the gas supply the stones must be gas-permeable in the same manner. Moreover, the gas-permeability of the stones during their service life, that is during the entire life of the furnace, must remain substantially constant.
The known gas-permeable stones of porous refractory material do not satisfy these requirements. Their stability in refining vessel is considerably smaller than the stability of the surrounding casing material. Thus, the porous stones embedded in the bottom of an oxygen converter withstand less than 100 charges, whereas the stability of the lining itself is 500 charges and more. Furthermore, a discontinuous gas supply is not possible with the porous stones; the metal penetrates into the pores of the stone and hardens there. After switching on the gas supply, the stone is no longer sufficiently gas-permeable.
In the patent application LU 81,208 applicants disclose a device which can be inserted into the bottom of a metal treatment vessel for blowing a treatment gas into a metal bath, which has a considerably improved stability with respect to the hitherto known gas-permeable stones, and which permits the blowing of the desired gas quantities. This device essentially consists of a refractory gas-permeable structural unit, whereby in an axial direction of the refractory material a plurality of flat, wave-like, pipe-like or wire-like metallic separating members of a low wall thickness are embedded. In accordance with one embodiment, this structural unit consists of steel sheet metal and segments or strips of refractory material in alternating disposition.
For manufacturing such a structural unit, it is necessary to cut a prefabricated block of refractory material into the required strips or segments, which is a very expensive manufacturing process. Since the segments have as a rule a very small thickness and a great length, the segments manufactured by compressing refractory "material" are not sufficiently easy to handle and warp when they are subjected to burning.